Existing X-ray imaging systems are known to use an image intensifier (II) to obtain an intensified visible image representing the X-rays detected at the detector side of the image intensifier. The visible image can be captured with a camera-lens assembly (CLA) resulting in a digital dataset that can be visualized on e.g. a display device and/or processed in many different ways. The digital datasets can be created and used for many purposes, including medical applications, machine vision, and non-destructive testing. The combination of the image intensifier and CLA is called IITV (‘image intensifier-television camera’).
An example CLA is the PEARL family of CLA's for digital IITV X-ray chains (Adimec Advanced Image Systems BV, Eindhoven, The Netherlands). This family of products comprises the PEARL-F for low dose fluoroscopy for e.g. universal radiography, and, amongst others, vascular applications, the PEARL-S for e.g. mobile C-arm systems (with image rotation) for surgery systems, and the PEARL-E for e.g. high dose exposure (spot imaging) and fluoroscopy for universal radiography and, amongst others, cardiovascular applications. The technique of fluoroscopy can be performed in a continuous X-ray mode, in which a low X-ray dose is generated continuously, or in a pulse X-ray mode, in which a sequence of X-ray pulses is generated. The CLA has a motorized iris and a Charge-Coupled Device (CCD) as the image sensor. This type of CLA can generate, for example, 1024×1024 pixels images with 12-bit pixels and has a dynamic range of 62 dB.
The amount of light that is produced by the image intensifier can vary depending on the X-ray dose. The known CLA has a motorized iris and/or a variable neutral density (ND) filter, to adapt to such differing brightness conditions. By varying the diaphragm and/or the ND filter, the dynamic range of the captured image is made as large as possible, while avoiding overexposure and/or clipping.